Known is a technology of performing arc welding with respect to a workpiece that is a welding target while causing a welding torch to automatically track a weld line of the workpiece. Such an automatic arc welding device needs to perform a control operation in which while causing the welding torch to move in a cyclic manner in a width direction of a groove of the workpiece with a specified weaving width and a specified torch height, the welding torch is caused to move such that beads are obtained in a direction along the weld line of the workpiece. In this control operation, it is necessary to understand a relative positional relation between the welding torch and the weld line of the workpiece. For example, a position sensor, such as a laser sensor, may be provided on the welding torch. However, the position sensor is expensive, and in the case of welding a narrow portion, the position sensor may become an obstacle.
Here, in a welding operation taking advantage of the characteristics of welding arc and using an arc sensor that does not require an additional device around the welding torch, the position of the welding torch is understood by detecting an arc welding current or arc voltage generated between the workpiece and an electrode projecting from a tip end of the welding torch and calculating a distance between a tip end of the electrode and the workpiece. Specifically, weld line tracking can be controlled by comparing welding current values or arc voltage values at both ends of weaving, and the torch height can be controlled by comparing the welding current value or arc voltage value in the weaving with a target value.
Further, also known is a method of controlling the weaving width in order to realize an appropriate weaving width with respect to a groove width of the workpiece (see PTL 1, for example). In this case, a control operation of increasing or decreasing the weaving width by comparing the welding current value or arc voltage value at the end portion of the weaving with the target value is performed.